Many large electronic systems, e.g., compute servers, disk storage arrays, telecommunications installations, etc., require large amounts of operating power and this operating power must be highly reliable. A common approach for system designers is to implement a system power supply as a plurality of smaller power supply modules. The outputs of the plurality of smaller power supply modules are connected together in parallel to provide the operating power required. Usually there are more power supply modules in the system power system than required to supply the existing load. This arrangement enables removal (e.g., unplugging) of faulty power supply modules while the electronic system is operational and may not impact the operation thereof. Replacement power supply modules, e.g., new or repaired, may be plugged back into the system power supply to maintain a desired amount of redundant power supply capacity.
When the power supply module outputs are connected in paralleled, it is impossible to insure that each parallel connected power supply module has the same output voltage. There are always tolerances in wiring, voltage references, temperatures, and other factors that may cause the output voltages to differ slightly between the power supply modules. Therefore one or more of the power supply modules having a slightly higher output voltage, will tend to supply the bulk of the system load. Therefore, some of the power supply modules may be operating at full power while others may be providing almost no power. The power supply module operating at full power will be hotter and therefore more failure prone. The power supply modules that are operating at full power are “saturated” and can not supply additional power if there is a load transient. Also, the other power supply modules that are supplying little or no power may not be operating in an ideal state for a switch mode converter power supply. A lightly loaded power supply module may not have a desired response to a transient load. For optimum reliability and performance, each of the power supply modules should carry an evenly distributed share of the system load.
Attempts at achieving an evenly distributed share of the system load between the power supply modules has been implemented by using analog signaling over a “party-line” between power supply modules. This party-line may be implemented where each power supply module drives a voltage through a resistor onto a single wire bus. The applied voltage is a representation of the power level at which that power supply module is operating. All of the power supply modules monitor this bus voltage which is an arithmetic average of all of the voltages applied from the power supply modules. This bus voltage represents the average power each of the power supply modules should apply to the load. Each power supply module's control circuitry then drives its output voltage to achieve this average power value, thus creating a load-balanced power supply system.
For example, a “master” device (controller) may monitor the total load and then may issue analog commands to each of the power supply modules in an effort spread the workload evenly among these power supply modules. The master control device may provide a voltage that represents a target power output goal for each power supply module. This master control device control voltage to each of the modules may be an analog voltage that may be used to adjust the power supply module's reference voltage and thereby may adjust the resultant output power from the module. This type of power flow signaling control may be prone to a single point failure. If the master controller fails, the power supply system may become unusable and/or inoperative.
The power supply modules reside in a noisy environment, wherein existing techniques for communicating load share information between power supplies are very sensitive to noise and require specialized circuitry to implement. Most modern technology power supplies use switching regulators that are controlled with digital circuits. In order to generate an analog control signal, a digital-to-analog converter (DAC) is needed to create an analog power indication signal. DACs may be large and expensive to implement into a power supply system. Digital techniques could offer better noise immunity, but existing digital techniques use communications protocols that are sensitive to noise transients present in the switching power supply modules.